This invention relates to seats and particularly to seats used in applications where the seat is subjected to vibrations such as in heavy trucks and off-highway construction equipment. In such equipment, the driver's seat is generally suspended for isolation of vibrations. To provide additional comfort, it is often desirable that the seat back be capable of being tilted over a small range, such as about 15.degree. . One widely used adjuster mechanism incorporates gears and relies on the gear ratio and friction to maintain a desired seat back angle adjustment. Although such a mechanism works well in light trucks and vans, it is unsuitable for heavy duty vehicles where vibration can cause rotation of the gearing and movement of the seat back. The gear type adjuster mechanism also requires substantial effort on the part of the seat occupant to rotate its parts against their inherent friction. Furthermore, several turns of the adjuster knob are needed to provide a 15.degree. seat back angle adjustment.
It is among the objects of the present invention to provide a seat back adjuster mechanism which provides positive locking, requires little force to operate, is simple and economical to manufacture, and can be moved throughout its range of adjustment with a single twist of the operator's wrist.